1. Field of the Invention
This invention relates to anatomically shaped disposable dental impression trays formed of thermoplastic material and having reinforced edges and cross-bracing.
2. Discussion of the Background Art
To form an accurate impression of a dentulous or edentulous alveolar ridge, in the course of producing a male model of desired oral tissues, conventional practice involves the use of commercially available initial impression trays for use with either the maxillary or the mandibular alveolar ridges and contiguous tissues, in either dentulous or edentulous cases. These trays are available in a range of sizes so that one which makes an approximate fit with the patient's mouth shape and size may be chosen for use. They have a cross-section characterized by a channel with two normally extending walls so that they will surround the ridge of which an impression is to be formed. The contours of these trays are not anatomical in the sense that they are adapted to abut or lie in close proximity to the gum area surrounding the ridge, but rather a tray is chosen which fits within the patient's mouth and loosely surrounds the tooth or gum section. The tray is constructed to fit over the general structures of the dental anatomy and constructed in many lengths, widths and with varying degrees of curvature, and is used to transport and hold in place a substance, often referred to as impression material and which, when hardened, creates an accurate negative image of the structures in the mouth.
These stock trays are typically formed of aluminum, stainless or plated steel, hard plastic, or other material that may be bent or trimmed at the edges to improve the fit to an individual patient. Impression material is placed in the tray and a female cast of the required area is formed. This cast is then typically used to form an initial male model of the patient's mouth section either in the dental office or in a separate dental laboratory. The dental office or laboratory then uses this male model to form a custom final impression tray out of a plastic material. This tray is anatomical in that it closely adapts to the male model and is relieved in the muscle attachments and other contiguous tissue areas.
The dentist then uses this custom tray to form a final impression of the required area by placing a high definition, settable, impression material such as polyvinylsiloxane, polyether or the like, into the impression tray. This conventional practice typically requires two separate procedures with two patient appointments and is relatively expensive and time consuming.
A number of alternative means for forming final impressions have been proposed to overcome these recognized inadequacies of the conventional procedure. For example, several forms of stock trays have been devised which may be shaped exteriorly of the mouth to improve the accuracy of initial impressions.
When a patient is edentulous (i.e. has no teeth in the dental arch), a dental tray designed with a high degree of curvature to take an impression of the teeth and immediate surrounding tissue is not adequate for this function. Using such a tray results in impressions of the dental ridge is inaccurate and not suitable for full denture construction. Disposable dental impression trays presently available have shorter heights or lesser arches, more suitable to the contours of the edentulous dental ridges but distort easily under the load of impression material when transported and placed in the mouth under sufficient pressure to seat or mold the impression. When such a tray is removed from the mouth and the seating pressure is relieved, the tray springs back to its unstressed form and bends or distorts the impression. The flexibility of the tray is worsened as the size of the back end flanges increase and the dental ridge flattens.
This is more evident with disposable dental impression trays for impression taking of the mandible where the tray's horse-shoe or U-shaped, allowing for a space to accommodate the tongue, markedly reduces the rigidity of the dental tray. The distortion of the impression has the consequence of ultimately causing a newly made denture to be poorly fitting.
There is, thus, a need to develop an inexpensive disposable dental tray for the edentulous ridge that is both thin and sufficiently rigid to minimize distortion of the tray during impression taking of edentulous dental ridges and subsequent distortion of the impression resulting therefrom.